First, let's establish some basic understandings before moving on to the main points on this topic:
Let's begin with what Stephen Covey calls the "Emotional Bank Account". It's the simple idea that our interactions with others create a certain emotional exchange that can be thought of in terms of a balance sheet. Someone does something good for you - that equals points for them. Someone does something really good for you - that equals a huge deposit. Someone says a hurtful thing, that withdraws from the "account". It's an easy idea.
In our interactions with people, our emotional "account balance" will determine, at least in part, what types of behavior are appropriate or inappropriate. We may tease our best friend about a bad sunburn or a bad haircut but we would not presume to do the same with someone we had just met. Why? Because we have not established a working relationship with them. We havn't put anything in that particular "account" yet. Whereas, with a long time friend, we may indulge in some friendly teasing at their expense because we know that they are capable of taking it from us and that they will not assume malicious motives on our part.
In addition to the emotional economy between two people, outside conditions factor into appropriate decision making. Though two people may be able to normally tease each other, one would not presume to do so if one's friend had just had their car stolen or perhaps experienced a death in the family. Why? Because the context involved would influence the other person such that a certain "weight" will necessarily be added to the interactions they happen to experience during that time of influence.
In addition to momentary outside contexts, there are also "chronic" contexts that will influence certain types of interaction consistently. For example, say you know someone who is an outstanding friend but they happen to be in a position in life where money does not come easy for them. They have to work very hard for what they get and any little expense is much more pressing to them than it would be for you. Such a circumstance may affect what types of activities you would engage in with that person. You would probably not presume to consistently invite them to the "golf course" because you know that they can't afford to pay the fees and, as a result, the good intent of offering such an invitiation is overridden by the fact that it would more remind the person of their financial straits rather than express a sense of comraderie on your part. In addition, if such a friend knows that you are aware of his or her situaion, that person may see it as you making fun of their personal struggles. Such would be a huge withdrawal.
One of the main problems with practical jokers is that they tend to see their intent as the governing idea involved in the "joking" situation regardless of any emotional bank account issues or outside circumstances involved. Now, if the emotional economy is fine and the "joke" is not insensitive to any outside circumstances that may be weighing on the person or persons involved, then there is potentially no problem with a practical joke. In fact, it can actually create a really funny memory that serves as a talking point in the friendship afterwards. However, if the "joke" does come up against either of these two issues, then it will not be funny at all and it may actually hurt the relationship.
A good indicator of whether or not the person doing the "joking" really is a friend or not can be found in how they react when they realize that they have encountered an emotional economy issue or an important outside context in the process of what they were trying to do. If I were attempting to play a practial joke on someone and then I became aware of how such a joke may be really hurting my relationship with them, then, if I care about the friendship, I will apologize and express how I didn't know it would be such a big deal. I would respect the perception of the person receiving the joke.
On the other hand, insensitive "jokers" selfishly justify their actions regardless of the contexts or emotional economies involved. They argue that the person they are hurting is just "too sensitive" or that they "just can't take a joke." Such justifications are ignorant and reveal a selfishness that runs counter to the empathy and understanding inherent in a true friendship. True friends can joke - but, true friends also realize that not all times, places, and circumstances are appropriate for such.
So, what are we to conclude about practical jokes? Well, for starters, true friends will check themselves. They will survey the situation and see if their joke will not actually hurt anybody. They will make sure that they have a robust enough emotional economy to compensate for the withdrawal their joke is about to make and they will make sure that they are not being potentially insensitive to weighty outside circumstances. In contrast, false friends just "act first and ask questions later" and, if it turns out that they have actually hurt someone, they will respond with an attack on the recepient's "sense of humor" rather than with a friendly apology.
Since none of us happen to be omniscient, we cannot always know what is going on in the lives of others. Thus, we should be extremely hesitent with regard to practical jokes because we never know just when an outside circumstance may be a problem. (If someone has just found out that they will be laid off from their job, the last thing they need to encounter when they come home from work is some sort of "joke" involving their yard being trashed.)
If we do cross one of these boundaries inappropriately (even when we thought we were on safe ground) we should apologize immediately. Such sensitivity can actually strengthen a relationship because it reflects an inner sense of concern for others. On the other hand, if a person playing a practical joke realises that their joke was inappropriate and, yet, chooses to respond with defensiveness and attacks about the other person's "lack of a sense of humor", then such a person is not really a friend - they are a nuisance.
Back to My Observations.